Fuel-injection valve

ABSTRACT

A fuel injector for fuel-injection systems of internal combustion engines includes an excitable actuator, a valve needle, which is in operative connection with the actuator and acted upon in a closing direction by a restoring spring to actuate a valve-closure member, which, together with a valve-seat surface formed on a valve-seat body, forms a sealing seat; and having at least one spray-discharge orifice which is formed in the valve-seat body. A guide region, which is formed in the valve-seat member and in which the valve-closure member is guided, is configured in such a way that it tapers conically in a flow direction of the fuel.

FIELD OF THE INVENTION

The present invention relates to a fuel injector.

BACKGROUND INFORMATION

German patent document no. 198 04 463 A1, for instance, refers to afuel-injection system for a mixture-compressing internal combustionengine having externally supplied ignition is known, which includes afuel injector that injects fuel into a combustion chamber formed by apiston/cylinder construction and has a spark plug which projects intothe combustion chamber. The fuel injector is provided with at least onerow of injection orifices distributed across the circumference of thefuel injector. By a selective injection of fuel via the injectionorifices, a jet-controlled combustion method is implemented by at leastone jet in that a mixture cloud is formed.

A particular disadvantage of the fuel injector known from theaforementioned publication may be the deposit formation in thespray-discharge orifices. These deposits clog the orifices and cause anunacceptably high reduction in the flow rate through the injector, whichleads to malfunctions of the internal combustion engine.

SUMMARY OF THE INVENTION

The fuel injector according to the exemplary embodiment of the presentinvention may have the advantage that a guide region in the valve-seatbody, which conically tapers in the discharge direction of the fuel,allows hydraulic self-centering of the valve-seat body on the sealingseat during closing of the fuel injector. This prevents post-sprays andthus deposits in the region of the spray-discharge orifices and preventsan unacceptable flow reduction.

Given an angle of the guide region of 2° to 7.5° with respect to theperpendicular line, spherical valve-closure members, which are able tobe produced and installed very easily and inexpensively, mayadvantageously be used.

It is also advantageous that play existing between the valve-closuremember and the valve-seat body has different magnitudes in the open andclosed state of the fuel injector; this causes a slight impact pressureto build up, which leads to automatic centering of the valve-closuremember.

Furthermore, it is advantageous if the sealing seat and the guide regionare drilled and ground in one working step in a joint clamping, usingthe same axis of symmetry.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic section through an exemplary embodiment of afuel injector according to the present invention.

FIG. 2 shows a schematic section through the exemplary embodiment of thefuel injector according to the present invention, in region II in FIG.1.

DETAILED DESCRIPTION

An exemplary embodiment of the present invention is described below byway of example. Identical parts have been provided with matchingreference numerals in all of the figures.

An exemplary embodiment of a fuel injector 1 according to the presentinvention, shown in FIG. 1, is designed in the form of a fuel injector 1for fuel-injection systems of mixture-compressing internal combustionengines having externally supplied ignition. Fuel injector 1 isparticularly suited for the direct injection of fuel into a combustionchamber (not shown) of an internal combustion engine.

Fuel injector 1 is made up of a nozzle body 2 in which a valve needle 3is positioned. Valve needle 3 is in operative connection with avalve-closure member 4, which cooperates with a valve-seat surface 6positioned on a valve-seat body 5 to form a sealing seat. Fuel injector1 in the exemplary embodiment is an inwardly opening fuel injector whichhas at least one—in the exemplary embodiment, two—spray-dischargeorifice(s) 7.

Valve-closure member 4 is guided in valve-seat body 5 by gimbals.According to the exemplary embodiment of the present invention, a guideregion 37 of valve-seat body 5 has a design that tapers conically in thespray-discharge direction. Beveled sections 38 on valve-closure member 4guide the fuel that is flowing through fuel injector 1 to the sealingseat and spray-discharge orifices 7. A detailed description of themeasures according to the invention may be gathered from FIG. 2 and thespecification.

Seal 8 seals nozzle body 2 from an outer pole 9 of a solenoid coil 10.Solenoid coil 10 is encapsulated in a coil housing 11 and wound on acoil brace 12, which rests against an inner pole 13 of solenoid coil 10.Inner pole 13 and outer pole 9 are separated from one another by aconstriction 26 and interconnected by a non-ferromagnetic connectingpart 29. Solenoid coil 10 is energized via a line 19 by an electriccurrent, which may be supplied via an electrical plug contact 17. Aplastic extrusion coat 18, which may be extruded onto inner pole 13,encloses plug contact 17.

Valve needle 3 is guided in a valve-needle guide 14, which isdisk-shaped. A paired adjustment disk 15 is used to adjust the (valve)lift. Armature 20 is on the other side of adjustment disk 15. Via afirst flange 21, it is in force-locking connection to valve needle 3,which is connected to first flange 21 by a welded seam 22. Braced onfirst flange 21 is a restoring spring 23, which is prestressed by asleeve 24 in the present design of fuel injector 1.

Fuel channels 30, 31 and 32 run in valve-needle guide 14, armature 20and along a guide element 36. The fuel is supplied via a central fuelsupply 16 and filtered by a filter element 25. A seal 28 seals fuelinjector 1 from a fuel distributor line (not shown further), and anadditional seal 37 seals it from a cylinder head (not shown further).

On the spray-discharge side of armature 20 is an annular damping element33 made of an elastomeric material. It rests on a second flange 34,which is joined to valve needle 3 by force-locking via a welded seam 35.

In the quiescent state of fuel injector 1, armature 20 is acted upon byrestoring spring 23 against its direction of lift, in such a way thatvalve-closure member 4 is held in sealing contact on valve-seat surface6. In response to excitation of solenoid coil 10, it generates amagnetic field that moves armature 20 in the lift direction, counter tothe spring force of restoring spring 23, the lift being predefined by aworking gap 27 that occurs in the rest position between inner pole 12and armature 20. First flange 21, which is welded to valve needle 3, istaken along by armature 20, in the lift direction as well. Valve-closuremember 4, being connected to valve needle 3, lifts off from valve seatsurface 6, and fuel guided, via fuel channels 30 through 32, isspray-discharged through spray-discharge orifice 7.

If the coil current is interrupted, following sufficient decay of themagnetic field, armature 20 falls away from inner pole 13 due to thepressure of restoring spring 23, whereupon first flange 21, beingconnected to valve needle 3, moves in a direction counter to the liftdirection. Valve needle 3 is thereby moved in the same direction,causing valve-closure member 4 to set down on valve seat surface 6 andfuel injector 1 to be closed.

In a part-sectional view, FIG. 2 shows the detail of fuel injector 1configured according to the exemplary embodiment of the presentinvention, which is denoted by II in FIG. 1.

As already mentioned before, valve-closure member 4 is guided invalve-seat body 5 by gimbals. In general, inwardly opening fuelinjectors, especially in conjunction with large seat angles, have thedisadvantage that valve needle 3 does not immediately close fuelinjector 1 completely after striking the sealing seat. This causes acertain fuel quantity to be post-injected, which is undesirable. Sincethis is still happening in the combustion phase of the fuel/air mixturein the combustion chamber, the flame front penetrates as far as thespray-discharge orifices 7. This causes an increase in deposits fromcombustion products in the region of spray-discharge orifices 7,resulting in clogging of spray-discharge orifices 7 and thus anunacceptably high reduction in the flow rate through fuel injector 1.

As a counter measure according to the exemplary embodiment of thepresent invention, a guide region 37 of valve-seat body 5 in whichvalve-closure member 4 is guided tapers conically in the flow direction.In this way the guide play between valve-closure member 4 and valve-seatbody 5 differs in its magnitude as a function of the lift of valveneedle 3. When fuel injector 1 is closed, the guide play is at itslowest and occurs in an order of magnitude of approximately 4 μm. Atmaximum lift of valve needle 3 in the open state of fuel injector 1, theguide play is considerably greater and amounts to 8 μm, for instance.The opening angle of conical guide region 37 may lay between 4° and 15°.

If fuel injector 1 is closed, the conicalness of guide region 37 causeshydraulic self-centering of valve-closure member 4. During its axialmovement in the flow direction, valve-closure member 4 displaces fuelthat is present in guide region 37. The fuel thereby accumulates sinceguide region 37 becomes narrower in the flow direction. As aconsequence, a pressure bolster is formed in the region of thevalve-closure member in guide region 37, which hydraulically centersvalve-closure member 4 within guide region 37. Immediately after theclosing operation, valve-closure member 4 thus seals across the entiresealing circumference at valve-seat surface 6 with respect to thesealing seat. Without this measure, valve-closure member 4 would strikevalve-seat surface 6 eccentrically and be centered only after a certainperiod of time by the action of a closing force exerted by restoringspring 23 via valve needle 3.

For the precise centering of guide region 37, valve-seat surface 6 andguide region 37 must be drilled and ground with a shared axis ofsymmetry, which may be together and in one clamping in a tool machine.

The present invention is not limited to the exemplary embodiments shown,but is also applicable to any other designs of fuel injectors 1.

1-11. (canceled)
 12. A fuel injector for a fuel-injection system of aninternal combustion engine, comprising: a restoring spring; a valveclosure member; an energizable actuator; a valve needle, which is inoperative connection with the actuator and acted upon in a closingdirection by the restoring spring to actuate the valve-closure member,which, together with a valve-seat surface formed on a valve-seat body,forms a sealing seat; and at least one spray-discharge orifice, which isformed downstream from the sealing seat, wherein a guide region, whichis formed in the valve-seat body and in which the valve-closure memberis guided, tapers conically in a flow direction of fuel.
 13. The fuelinjector of claim 12, wherein the guide region is formed on an inflowside of the sealing seat.
 14. The fuel injector of claim 12, wherein, asa result of the conicalness, an impact pressure prevails in the fuelthat is present in the guide region.
 15. The fuel injector of claim 14,wherein the impact pressure in the guide region leads to a hydraulicself-centering of the valve-closure member in the guide region.
 16. Thefuel injector of claim 12, wherein a cone-opening angle of the guideregion is between 4° and 15°.
 17. The fuel injector of claim 12, whereinguide play existing between the valve-closure member and the valve-seatbody amounts to approximately 4 μm in a closed state of the fuelinjector.
 18. The fuel injector of claim 12, wherein guide play existingbetween the valve-closure member and the valve-seat body amounts toapproximately 8 μm in an open state of the fuel injector.
 19. The fuelinjector of claim 12, wherein the valve-closure member has a sphericaldesign.
 20. The fuel injector of claim 12, wherein the valve-seat memberis connected to the valve needle by welding or soldering.
 21. The fuelinjector of claim 12, wherein the valve-closure member has beveledsections in the guide region.
 22. The fuel injector of claim 12, whereinboth the guide region and the sealing seat are jointly drilled andground with a shared axis of symmetry, in one clamping.